PMSL - We will end up with Haz Area classifications next for a covered car with battery on a conditioner......I don't think there is much chance you will ever reach an explosive mixture under normal circumstances, not much to worry about.
Hmmm.... Hydrogen 4%LEL let me see......... haha!
I wonder what happens to the charging gases with a car cover on? It would permeate a cloth cover I guess, but might cause a nasty surprise with a waterproof cover, especially with the static they produce when removed. Paranoid?